Thursday, September 17, 2009

More on Velociraptor Feet

I love the outdoors. I love rocks, big and small. I like feeling them, and I like clambering over them. But to see someone scaling a sheer wall, hundreds or thousands of feet in the air, seizes my breath. I can't imagine possessing the kind of focus it would take to perform such a feat. A common occurence in my dreams is a terrible weakness in my hands - I throw a punch and it's no more than a bop from a pillow. Something in me doubts the power in my hands, and I can't help but think they would fail me, lose grip on whatever fissure or outcrop they were holding, and I'd fall to the ground, vulture food.

Image copyright American Museum of Natural History

The above fossil, a national treasure of Mongolia, is such a rare thing that to even imagine it seems unimaginable: an actual interaction between animals, fossilized. It's a protoceratops and a velociraptor, fighting. It's believed that in the midst of their struggle, the pair were either buried in a collapsed sand dune or overtaken in a sand storm.

In the recent paper on dromaeosaur claws, Manning et al add another possible factor in the death grip. They cite a characteristic I had no idea modern perching birds possessed. And in light of the mild neurosis I mention in the opening paragraph, I'm envious.

I've always taken it for granted that some birds sleep while perched. They just do. I've never given it a second thought. It turns out that the bird doesn't have to give it any thought, either. They land on a limb, their foot grasps it. No special effort needed. The tendons that flex their toes are modified so they automatically lock the foot around the branch. If I possessed a similarly built pair of hands, well, I wouldn't need to worry about losing my grip. I'd grab a handhold, my hand would lock on it, and I could doze off. I'm sure my adrenaline would prevent me from falling asleep, but I wouldn't fear falling from the rock face as I vainly counted (bighorn) sheep.

This paper suggests that dromaeosaur feet were adapted similarly, as they have a ridge on the bones that make up their sickle-claw toe. When a pack of them ambushed an Edmontosaurus, that fearsome claw on their second toe would just lock into it. They would go about their bloody business without giving thought to maintaining a hold on their prey.

Perhaps the Velociraptor in Mongolia's treasure was literally locked to that protoceratops. The proto had its attacker's arm in its beak. They'd fought each other to a stalemate. The raptor had nowhere to lock its jaws. As Manning writes, "Unable to reposition its limbs, it was impossible for the Velociraptor to deploy its jaws and finish the attack, like two boxers hugging each other and unable to throw a punch."